1. Field of the Invention
The invention relates to a structure that joins a junction box and an electrical component connector block. The structure is configured so as to prevent material failure of the connecting components on the junction box.
2. Description of the Related Art
Modern automobiles incorporate an increasing number of electrical components, which has resulted in an increase in the size of junction boxes used to connect electrical power and signal circuits, and increasingly complex junction box structures. As a result of this tendency toward larger and more complex junction boxes, and the requirement that junction boxes be capable of flexibly adapting to changes in the layout of circuits connected thereto, connecting structure must be provided to connect relay blocks, fuse blocks, and similar components to the junction box.
FIGS. 8A and 8B illustrate a conventional connecting structure for joining a junction box 1 and a relay block 4. In this structure, relay block 4 is joined to a junction box frame 2 through an insertion portion 5 located on an external sidewall 4b of relay block 4, and a receiver bracket 3 located on an external sidewall 2a of junction box frame 2. Relay block 4 is attached to junction box frame 2 by aligning insertion portion 5 over receiver bracket 3 and sliding relay block 4 downward. Attachment is complete when insertion portion 5 slides downward to a fully inserted position within receiver bracket 3, such that relay block 4 is aligned adjacent to junction box 1. A relay 4a can then be inserted into the upper surface of the attached relay block 4.
With relay block 4 attached to the junction box 1 in an adjacently aligned position, the force required to insert relay 4a into the relay block is applied as a leveraged load to receiver bracket 3 and insertion portion 5. As shown in FIG. 8C, external sidewall 2a of receiver bracket 3 is prone to material failure when a load greater than that required for insertion of the relay 4a is applied to the connecting components. If frame 2 of the junction box 1 is made from a glass impregnated resin, the connecting structure may fail more easily as a result of a load concentrated at a single point. The leverage force becomes more pronounced and the potential for material failure increases when multiple rows of relays 4a are installed onto the relay block 4, particularly during insertion of the outer row of relays 4a. 
Further, the application of an externally induced shock, such as a force resulting from the junction box 1 being dropped, or from other objects striking or applying force to the relay block 4, can induce the material failure of sidewall 2a and receiver bracket 3 on junction box frame 2. This type of failure is especially likely if frame 2 is molded from a glass impregnated resin. Moreover, because junction box 1 is a large and complex structure that costs more to produce than an attached electrical component connector block, such as relay block 4, the replacement cost of the junction box is higher than that of the relay block.
The present invention has been made in view of the above-described problems. Accordingly, it is an object of the present invention to provide a structure for joining an electrical component connector block, such as a relay block, fuse block, or similar component, to a junction box in adjacent alignment, wherein the connecting structure is not prone to material failure, and wherein the more expensive junction box will not incur material failure in the event that excessive force is applied to the connecting structure.
According to one aspect of the present invention, there is provided connecting structure for adjacently joining a junction box and an electrical connector block, the connector block including a component receptacle portion on an upper surface thereof. The connecting structure includes a receiver bracket provided on a sidewall of the junction box, an insertion bracket provided on a sidewall of the connector block, and a groove formed in a base portion of the insertion bracket adjacent to the sidewall of the connector block. The groove forms a weakened portion of the insertion bracket, such that material failure occurs at the weakened portion of the insertion bracket under a condition in which an excessive force is applied to a joined junction box and connector block.
Because the groove on the connector block is the weakest point in the connecting structure and will be the origin of any material failure, only the connecting structure that is part of the connector block will suffer material failure in the event that excessive external force is applied to the connecting structure. This structure can thus prevent material failure of the more expensive junction box case.
According to a further aspect of the present invention, the groove is formed around an entire periphery of the base portion of the insertion bracket. The groove may also have a V-shaped cross section, for the desirable failure localization characteristics thereof.
The connecting structure may further include reinforcement ribs provided on the sidewall of the junction box below the receiver bracket. The provision of such reinforcing ribs increases the strength of the receiver bracket on the junction box against an excessive externally applied load, thus providing further assurance that an excessive load will not result in material failure of the junction box connecting component.
The connector block may be a relay block, and the component receptacle portion of the connector block may be configured to receive at least one relay inserted therein. The connector block may be a fuse block, and the component receptacle portion of the connector block may be configured to receive at least one fuse inserted therein.
According to a further aspect of the present invention, the connecting structure includes a protruding hook portion provided on the connector block. The hook portion is configured to connect to an upper edge of a sidewall of the junction box. The hook portion may be provided on the sidewall of said connector block. The hook portion distributes a force resulting from insertion of a component into the component receptacle portion of the connector block along the upper edge of the junction box sidewall. The groove may also be formed in a base portion of the hook portion adjacent to the sidewall of the connector block.
As this structure provides for a hook part that connects to the junction box case, the load applied by the insertion of components into the component receptacle will not only be distributed through the connecting structure, but also through the sidewall as a result of the hook part joined thereto. A structure is thus formed that is able to adequately resist loads incurred as a result of component insertion even though a groove has been provided around the base part of the insertion bracket at the connector block sidewall.